Add native self-hosted instance connection to fluxer_desktop

Trimmed monorepo checkout (fluxer_desktop + packages/voice_engine_v2 +
tools/ci) with a "Connect to a Different Server" menu item and popout
that lets the desktop app switch to any self-hosted Fluxer instance,
plus fixes for well-known discovery on single-domain self-hosted
deployments and a false-positive ERR_ABORTED on same-origin client
redirects during the switch. Defaults to chat.fluxr.chat and uses an
isolated userData directory from the official build.

fluxer_desktop/native/audio-mix/benches/mix.rs

@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+use std::hint::black_box;
+
+use criterion::{Criterion, criterion_group, criterion_main};
+use fluxer_audio_mix::{
+    AUDIO_OUTPUT_FRAMES, AudioMixSession, SourceRing, SourceRingConsumer, SourceRingProducer,
+};
+use fluxer_rt_thread::TickInfo;
+
+const BENCH_SOURCE_COUNT: usize = 8;
+
+fn build_session(source_count: usize) -> (Vec<SourceRingProducer>, AudioMixSession) {
+    assert!(source_count > 0);
+    let mut producers = Vec::with_capacity(source_count);
+    let mut consumers: Vec<SourceRingConsumer> = Vec::with_capacity(source_count);
+    for _ in 0..source_count {
+        let (producer, consumer) = SourceRing::create(8192, 48_000).expect("pair");
+        producers.push(producer);
+        consumers.push(consumer);
+    }
+    let session = AudioMixSession::new(consumers, AUDIO_OUTPUT_FRAMES).expect("session");
+    (producers, session)
+}
+
+fn synthetic_tick(index: u64) -> TickInfo {
+    let scheduled_ns = index * 21_333_333;
+    TickInfo {
+        tick_index: index,
+        scheduled_ns,
+        actual_ns: scheduled_ns,
+        lag_ns: 0,
+    }
+}
+
+fn fill_producers(producers: &mut [SourceRingProducer], frames: usize) {
+    assert!(!producers.is_empty());
+    assert!(frames > 0);
+    let payload: Vec<i16> = (0..frames).map(|n| ((n as i16) % 4096) - 2048).collect();
+    for producer in producers.iter_mut() {
+        let pushed = producer.try_push_slice(&payload);
+        assert!(pushed > 0);
+    }
+}
+
+fn bench_mix_tick(c: &mut Criterion) {
+    let mut group = c.benchmark_group("audio_mix_tick");
+    group.sample_size(50);
+    group.bench_function("mix_8_sources_1024_samples", |b| {
+        let (mut producers, mut session) = build_session(BENCH_SOURCE_COUNT);
+        let mut tick_index: u64 = 0;
+        b.iter(|| {
+            fill_producers(&mut producers, AUDIO_OUTPUT_FRAMES);
+            let result = session.tick(synthetic_tick(tick_index));
+            tick_index = tick_index.wrapping_add(1);
+            black_box(result);
+        });
+    });
+    group.finish();
+}
+
+criterion_group!(benches, bench_mix_tick);
+criterion_main!(benches);